Desalination machine

ABSTRACT

A compact and economical array of vertical tube evaporators is disclosed in a multi-effect process, for desalination of sea water, brackish water, and in general to any water with dissolved solids, in order to produce fresh water for oil offshore platforms, ships, and for some arid locations, using rejected waste heat of thermal machines. This invention is based on a concentric disposition of the evaporators or stages, having three different specially designed evaporators, which the first stage is a shell and tube evaporator built in a ring format, named Ring Shell And Tube Evaporator, including an internal shell, and having a vapour chamber above its upper tubesheet; the intermediate stage is a bundle of tubes in a ring format named Ring Bundle Evaporator, having a vapour chamber above its upper tubesheet; and the last stage that is a bundle of tubes in a circular arrangement named Cylindrical Bundle Evaporator.

FIELD OF THE INVENTION

The present invention relates to a distillation process using verticaltube evaporators in a multi effect process and is applicable todesalination of sea water, brackish waters and in general to any waterwith dissolved solids, in order to produce fresh water for oil offshoreplatforms, ships, and for some arid locations, using rejected waste heatof thermal machines.

BACKGROUND OF THE INVENTION

Multi-effect distillation (MED) process has been used in industry forjuice evaporation, to concentrate a substance, production of salts andfor salty and marine water distillation for fresh water production.

In the MED process, only a portion of the concentrate submitted to theheat transfer surfaces is evaporated. Each effect works in a differentpressure. The remaining liquid of each effect, normally called brine, isfed to the liquid tray of the next effect or stage, where part of itflashes into vapour. Produced vapour in one effect will give up heat toboil the liquid transferred to the next effect due to the temperaturedifference between them.

Normally the effects or stages have evaporators located in separatechambers, requiring a pipeline for conducting vapour from one stage tothe next, as shown in the U.S. Pat. Nos. 3,884,767, 3,261,766 e3,021,265.

SUMMARY

Intended to improve the performance and reduce the dimensions of thiskind of equipment, the present invention is developed assembling theseveral evaporators in a concentric disposition, using a shell and tubeexchanger for the first stage and a bundle of tubes for the succeedingstages, which are inserted one inside each other. Through thisconstructive arrangement, the following advantages are achieved:material reduction due to the absence of vapour pipelines; vapourfriction losses reduced to a minimum; smaller size due to thecompactness of the concentric disposition of evaporators; no heat lossin the inner stages; cost effectiveness.

This unit can also be used to concentrate a mixture, using lowtemperature evaporative process.

Fresh water makers are extensively used in oil offshore platforms andships, normally using the heat of exhausted gases of thermal machines.

The figures attached, are representative of four different models,showing their respective stages, all using the same constructivearrangement, here named concentric evaporators. The higher the number ofstages the lower the energy consumption per volume produced. The choicefor the number of stages, depend on the available heat, the fresh waterrate desired and of course the involved costs.

The unit can be designed to produce any desired flow rate, meanwhile itis usual for this kind of equipment to have a production flow rateranging from 5 until 120 m3/d.

The dimensions of a 60 m3/d desalinator have approximately 2.2 m heightand 1.2 m in diameter.

DESCRIPTION OF THE DRAWINGS

The different models will now be exemplified with reference to theaccompanying drawings briefly described hereafter.

FIGS. 1 to 9 are representative of the two stage model.

FIG. 1 is the elevation view in cross section of the two stage modeltotally assembled;

FIG. 2 is the top view of the first stage evaporator here named RingShell and Tube Evaporator;

FIG. 3 is the elevation view in cross section of the Ring Shell and TubeEvaporator;

FIG. 4 is the top view of the second stage evaporator, here namedCylindrical Bundle Evaporator, that is the ultimate stage;

FIG. 5 is the elevation view in cross section of the Cylindrical BundleEvaporator;

FIG. 6 is the bottom view of the floating head of the Cylindrical BundleEvaporator;

FIG. 7 is the top view of the condenser inserted into the superiorchamber;

FIG. 8 is the elevation view in cross section of the condenser;

FIG. 9 is the condenser front view;

FIGS. 10 to 15 are representative of the three stage model;

FIG. 10 is the elevation view in cross section of the three stage modeltotally assembled;

FIG. 11 is the elevation view in cross section of the first stage of thethree stage model, or the Ring Shell and Tube Evaporator;

FIG. 12 is the base support for intermediate stage, where A is the topview and B is a cross section view;

FIG. 13 is the elevation view in cross section of the intermediatestage, here named Ring Bundle Evaporator;

FIG. 14 is the bottom view of the floating head of the Ring BundleEvaporator;

FIG. 15 is the cross section of FIG. 14;

FIG. 16 is the elevation view in cross section of the four stage model.

DETAILED DESCRIPTION OF THE INVENTION

The following description is refereed to FIGS. 1 to 9, all related tothe two stage model, whose operational philosophy is extensive to theother models.

FIG. 1 shows the two stage model with its evaporators assembled in theconcentric arrangement where is observed that the second stage (FIG. 5)is assembled inside the first stage (FIG. 3), supported and bolted atthe flange 1 (FIG. 3). A gasket is used to avoid leakage. The upperchamber (FIG. 7) with the condenser 2 inserted into it, is assembledbolted in the same flange 1.

On FIGS. 2 and 3, is observed that the first stage is constituted of ashell and tube exchanger without part of the central tubes, here calledRing Shell and Tube Evaporator. The inner wall 3 encloses the hot waterthroughout the interior of the shell, returning for heating on outlet 5.

Salt water feeds the first stage on nozzle 6, passing throughout thechamber 7, and directs to the first stage tubes 8, receiving enough heatfrom hot water 4, until boiling. Heat is furnished so that only part ofthe water is vaporised in order to avoid excessive scales into thetubes. It is observed on FIG. 2 that the vapour chamber above theevaporator is enlarged in order to permit the passage of the vapour tothe condensation chamber 9 (FIG. 3).

Hot water temperature 4 is heated at maximum 88° C. in order to avoidexcessive scales into the tubes. Operating evaporative temperatureranges from 60 to 65° C. on the first stage and from 45 to 50° C. on thesecond. To obtain these evaporating temperatures, the pressure must beevacuated and controlled in the range of 20.0 to 25.0 kpa abs at thefirst stage and in the range of 9.9 to 12.4 kpa abs at the second stage.Vacuum is obtained by an eductor 10 (FIG. 1) that sucks the noncondensable gases like air and carbon dioxide through the first stagevacuum outlet 11, and second stage vacuum outlet 12. Salt water at aspecific designed pressure 13 (FIG. 1) is used to drive the eductor.

Boiling water and vapour rises into the tubes 8, splashing on the plate14 (FIG. 3). Vapour flows to the second stage evaporator tubes 15 (FIGS.1 and 5), here named Cylindrical Bundle Evaporator. Touching the tubewalls, the vapour condenses, giving up energy to boil the second stagesalt water. The condensate produced is collected on the bottom of thechamber 9 (FIG. 3) and pumped to a storage tank through the outlet 16,delivering sensible heat to the incoming salt water 6 through the bundle17, inside chamber 7.

Second stage is fed by the remaining not vaporised first stage saltwater, suctioned by the second stage lower pressure through tube 18,pouring into the tray 19, and flashing vapour. Tube 18 collects saltwater from the bottom of an extended pipe, in order to keep an adequatewater column, to avoid suction of vapour from the first stage. On thetray, water directs to the central tube 20, dropping to floating head21, feeding second stage tube bundle 15. Tray 19 and plate 14 preventrising salt water droplets to reach the demisters 22 (first stage) and23 (second stage). Both plate 14 as tray 19 are removable in order topermit access to the tube sheets.

Second stage fresh water is obtained through the vapour condensation oncondenser 2, being collected in the container 24. Through outlet nozzle25 (FIG. 1), condensate is pumped to reservoir. Inside condenser tubescirculates cold salt water through inlet nozzle 26 (FIG. 1), leaving onnozzle outlet 27. Here, stream 4 is derived in order to feed firststage. Returned salt water 28 is discharged.

Level is maintained on the first stage by the weir 29. In the same way,second stage level is maintained by weir 30. Salt water that overboardsweir 30 exits the unit through outlet 31, being suctioned by eductor 10(FIG. 1) to discharge 32 (FIG. 1).

Nominal flow rate is obtained through control valve 33 and flow meter 34(FIG. 1). Instruments as thermometers and manometers are used foroperational control, and a pressure safety relief valve 35 installed onthe first stage grants against over pressure.

A thin steel shell 36 (FIG. 5), here named armour, which is assembled intwo halves by flanges, encloses second stage tube bundle. The role ofthis armour is to direct the vapour to pass through the tubes, avoidingbeing suctioned directly to vacuum pipe 11 (FIG. 1). The welded edge 37(FIG. 5) supports the armour at the top of the first stage inner shell3. A gasket bonded bellow the edge avoids vapour leakage.

A cut 38 (FIG. 6) made at the bottom tube sheet and at the floating head21, permits the passage of the fixed vacuum pipe 11.

The following description is refereed to FIGS. 10 to 16 of the threestage model.

Three stages model (FIG. 10) has the same two stage constructivephilosophy, with a new intermediate stage included, here named RingEvaporator Bundle (FIG. 13), that becomes the second stage, and isinserted into the first stage. The cylindrical evaporator (FIG. 5),becomes now the third stage, and is inserted into the Ring EvaporatorBundle (FIG. 13).

The first stage of this model (FIG. 11) is similar to the two stagemodel, but the base 39 (FIG. 11) is now welded to the inner and outershells 40 and 41 respectively (FIG. 11), in order to have a reliablewatertight. At the centre of this base is welded a support 42 (FIGS. 11and 12), in order to hold and centralise the intermediate stage (FIG.13).

On this model, vacuum lines 43 and 44 (FIG. 1) and distillate outlets 45and 46, are located bellow the unit, in order to permit easy access ofsecond and third stages.

Heat exchange is accomplished through a 15 to 20° C. differentialtemperature between stages.

Ring Evaporator Bundle has also an armour 47 (FIG. 13), in order todirect the first stage vapour to its bundle 48. Floating head 49 has inthis way a ring format also, as shown on FIG. 14 (bottom view) and FIG.15 (section view). An internal shell (50) encloses and isolate thevapour inside this stage.

The material used in the unit needs to be corrosive resistant to saltwater as aluminium bronze, monel, copper nickel, and titanium.

Four stages model is represented in a section view on FIG. 16. Now,another Ring Evaporator Bundle is included, as an intermediate stage,compounding in this way the four stage model, and so on.

1. “Desalinization Machine”, comprising of a series of vertical tubebundles, each bundle compounding an evaporator or stage, supported andsealed by an upper and a bottom tube sheet, in a multi effect process,characterised by having the assembling of the stages in a concentricdisposition (FIGS. 1, 10 and 16), where the first stage is a shell andtube exchanger in a ring format, here named Ring Shell and TubeEvaporator (FIGS. 3 and 11) having a free space at the centre of thebundle, where is inserted the next stage or intermediate stage that is abundle of tubes in a ring format, here named Ring Bundle Evaporator,having also a free space in the centre (FIG. 12), where is inserted thenext stage that could be another intermediate stage or the last stagethat is a bundle of vertical tubes here named Cylindrical BundleEvaporator (FIG. 5).
 2. “Desalinization machine” according to claim 1,where the Ring Shell and Tube Evaporator (FIGS. 2 and 3) arecharacterized by having the following features: a) an internal wall 3;b) a vapour chamber above the upper tube sheet defined by an extensionof said internal wall 3 and a circumferential external wall 51 (FIG. 3)welded at the edge of the upper tube sheet, with a flange on the top tosupport the second stage; c) a number of circular supports (42) (FIG.11) equal to the number of stages less
 2. 3. “Desalinization machine”according to claim 1, where the Ring Bundle Evaporator is characterizedby having the following features: a)an internal wall 40 (FIG. 11); b) avapour chamber above the upper tube sheet defined by an extension ofsaid internal wall 40 and a circumferential external wall 52 (FIG. 13)welded at the edge of the upper tube sheet, with a flange on the top tosupport the succeeding stage; c) an external wall 47 (FIG. 5), herenamed armour that encloses the vapour inside the tube bundle; d) theupper tube sheet 30% larger in diameter than the bottom tube sheet. 4.“Desalinization machine” according to claim 1, where the CylindricalBundle Evaporator is characterized by having the following features: a)an external wall 36 (FIG. 13) here named armour that encloses the vapourinside the tube bundle; b) a tray 19 (FIG. 13) to collect salt waterfrom the preceding stage to directs this water to the central tube 20;c) the upper tube sheet 30% larger in diameter than the bottom tubesheet.